Balloon Network with Free-Space Optical Communication between Super-Node Balloons and RF Communication between Super-Node and Sub-Node Balloons

ABSTRACT

Exemplary embodiments may involve hierarchical balloon networks that include both optical and radio frequency links between balloons. An exemplary network system may include: (a) a plurality of super-node balloons, where each super-node balloon comprises a free-space optical communication system for data communications with one or more other super-node balloons and (b) a plurality of sub-node balloons, where each of the sub-node balloons comprises a radio-frequency communication system that is operable for data communications. Further, at least one super-node balloon may further include an RF communication system that is operable to transmit data to at least one sub-node balloon, where the RF communication system of the at least one sub-node balloon is further operable to receive the data transmitted by the at least one super-node balloon and to transmit the received data to at least one ground-based station.

RELATED APPLICATION

This patent application claims priority to U.S. application Ser. No.13/346,636, filed on Jan. 9, 2012, the contents of which are entirelyincorporated herein by reference, as if fully set forth in thisapplication.

BACKGROUND

Unless otherwise indicated herein, the materials described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

Computing devices such as personal computers, laptop computers, tabletcomputers, cellular phones, and countless types of Internet-capabledevices are increasingly prevalent in numerous aspects of modern life.As such, the demand for data connectivity via the Internet, cellulardata networks, and other such networks, is growing. However, there aremany areas of the world where data connectivity is still unavailable, orif available, is unreliable and/or costly. Accordingly, additionalnetwork infrastructure is desirable.

SUMMARY

In one aspect, an exemplary network system may include: (a) a pluralityof super-node balloons configured as super-nodes in a balloon network,wherein each super-node balloon comprises a free-space opticalcommunication system that is operable for data communications with oneor more other super-node balloons; and (b) a plurality of sub-nodeballoons configured as sub-nodes in the balloon network, wherein each ofthe sub-node balloons comprises a radio-frequency (RF) communicationsystem that is operable for data communications; wherein at least onesuper-node balloon further comprises an RF communication system that isoperable to transmit data to at least one sub-node balloon, wherein theRF communication system of the at least one sub-node balloon is operableto receive the data transmitted by the at least one super-node balloonand to transmit the received data to at least one ground-based station.

In another aspect, an exemplary network system may include a pluralityof balloons that collectively operate as a hierarchical balloon network,wherein the plurality of balloons comprise at least (a) a plurality offirst balloons and (b) a plurality of second balloons; wherein each ofthe first balloons comprises a free-space optical communication systemthat is operable for packet-data communication with one or more otherfirst balloons; wherein each of the second balloons comprises aradio-frequency (RF) communication system that is operable for datacommunications; and wherein at least one first balloon further comprisesan RF communication system that is operable to transmit data to at leastone second balloon, wherein the RF communication system of the at leastone second balloon is operable to receive the data transmitted by the atleast one first balloon and to transmit the received data to at leastone ground-based station.

These as well as other aspects, advantages, and alternatives, willbecome apparent to those of ordinary skill in the art by reading thefollowing detailed description, with reference where appropriate to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram illustrating a balloon network,according to an exemplary embodiment.

FIG. 2 is a block diagram illustrating a balloon-network control system,according to an exemplary embodiment.

FIG. 3 shows a high-altitude balloon, according to an exemplaryembodiment.

FIG. 4 is a simplified block diagram illustrating a balloon network thatincludes super-nodes and sub-nodes, according to an exemplaryembodiment.

FIGS. 5A and 5B show an area covered by a portion of a balloon network,according to an exemplary embodiment.

FIG. 6A shows coverage of an exemplary balloon network that spans anumber of defined geographic areas, according to an exemplaryembodiment.

FIG. 6B is a simplified illustration of a balloon cluster, according toan exemplary embodiment.

FIG. 6C shows the same balloon network spanning the same geographicareas as shown in FIG. 6A, according to an exemplary embodiment.

DETAILED DESCRIPTION

Exemplary methods and systems are described herein. It should beunderstood that the word “exemplary” is used herein to mean “serving asan example, instance, or illustration.” Any embodiment or featuredescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other embodiments or features. Theexemplary embodiments described herein are not meant to be limiting. Itwill be readily understood that certain aspects of the disclosed systemsand methods can be arranged and combined in a wide variety of differentconfigurations, all of which are contemplated herein.

I. Overview

Exemplary embodiments help to provide a data network that includes aplurality of balloons; for example, a mesh network formed byhigh-altitude balloons deployed in the stratosphere. Since winds in thestratosphere may affect the locations of the balloons in a differentialmanner, each balloon in an exemplary network may be configured to changeits horizontal position by adjusting its vertical position (i.e.,altitude). For example, by adjusting its altitude, a balloon may be ablefind winds that will carry it horizontally (e.g., latitudinally and/orlongitudinally) to a desired horizontal location.

Further, in an exemplary balloon network, the balloons may communicatewith one another using free-space optical communications. For instance,the balloons may be configured for optical communications usingultra-bright LEDs (which are also referred to as “high-power” or“high-output” LEDs). In some instances, lasers could be used instead ofor in addition to LEDs, although regulations for laser communicationsmay restrict laser usage. In addition, the balloons may communicate withground-based station(s) using radio-frequency (RF) communications.

In some embodiments, a high-altitude-balloon network may be homogenous.That is, the balloons in a high-altitude-balloon network could besubstantially similar to each other in one or more ways. Morespecifically, in a homogenous high-altitude-balloon network, eachballoon is configured to communicate with one or more other balloons viafree-space optical links. Further, some or all of the balloons in such anetwork may additionally be configured to communicate with ground-basedstation(s) using RF communications. Thus, in some embodiments, theballoons may be homogenous in so far as each balloon is configured forfree-space optical communication with other balloons, but heterogeneouswith regard to RF communications with ground-based stations.

In other embodiments, a high-altitude-balloon network may beheterogeneous, and thus may include two or more different types ofballoons (i.e., two or more types of balloons that function insubstantially different ways). For example, some balloons in aheterogeneous network may be configured as super-nodes, while otherballoons may be configured as sub-nodes. It is also possible that someballoons in a heterogeneous network may be configured to function asboth a super-node and a sub-node. Such balloons may function as either asuper-node or a sub-node at a particular time, or, alternatively, act asboth simultaneously depending on the context. For instance, an exampleballoon could aggregate search requests of a first type to transmit to aground-based station. The example balloon could also send searchrequests of a second type to another balloon, which could act as asuper-node in that context. Further, some balloons, which may besuper-nodes in an exemplary embodiment, can be configured to communicatevia optical links with ground-based stations and/or satellites.

In an exemplary configuration, the super-node balloons may be configuredto communicate with nearby super-node balloons via free-space opticallinks. However, the sub-node balloons may not be configured forfree-space optical communication, and may instead be configured for someother type of communication, such as RF communications. In that case, asuper-node may be further configured to communicate with sub-nodes usingRF communications. Thus, the sub-nodes may relay communications betweenthe super-nodes and one or more ground-based stations using RFcommunications. In this way, the super-nodes may collectively functionas backhaul for the balloon network, while the sub-nodes function torelay communications from the super-nodes to ground-based stations.

II. Exemplary Balloon Networks

FIG. 1 is a simplified block diagram illustrating a balloon network 100,according to an exemplary embodiment. As shown, balloon network 100includes balloons 102A to 102F, which are configured to communicate withone another via free-space optical links 104. Configured as such,balloons 102A to 102F may collectively function as a mesh network forpacket-data communications. Further, at least some of balloons 102A and102B may be configured for RF communications with ground-based stations106 via respective RF links 108. Yet further, some balloons, such asballoon 102F, may be configured to communicate via optical link 110 withground-based station 112.

In an exemplary embodiment, balloons 102A to 102F are high-altitudeballoons, which are deployed in the stratosphere. At moderate latitudes,the stratosphere includes altitudes between approximately 10 kilometers(km) and 50 km altitude above the surface. At the poles, thestratosphere starts at an altitude of approximately 8 km. In anexemplary embodiment, high-altitude balloons may be generally configuredto operate in an altitude range within the stratosphere that hasrelatively low wind-speeds (e.g., between 5 and 20 miles per hour(mph)).

More specifically, in a high-altitude-balloon network, balloons 102A to102F may generally be configured to operate at altitudes between 18 kmand 25 km (although other altitudes are possible). This altitude rangemay be advantageous for several reasons. In particular, this layer ofthe stratosphere generally has relatively low wind speeds (e.g., windsbetween 5 and 20 mph) and relatively little turbulence. Further, whilethe winds between 18 km and 25 km may vary with latitude and by season,the variations can be modeled in a reasonably accurate manner.Additionally, altitudes above 18 km are typically above the maximumflight level designated for commercial air traffic. Therefore,interference with commercial flights is not a concern when balloons aredeployed between 18 km and 25 km.

To transmit data to another balloon, a given balloon 102A to 102F may beconfigured to transmit an optical signal via an optical link 104. In anexemplary embodiment, a given balloon 102A to 102F may use one or morehigh-power light-emitting diodes (LEDs) to transmit an optical signal.Alternatively, some or all of balloons 102A to 102F may include lasersystems for free-space optical communications over optical links 104.Other types of free-space optical communication are possible. Further,in order to receive an optical signal from another balloon via anoptical link 104, a given balloon 102A to 102F may include one or moreoptical receivers. Additional details of exemplary balloons arediscussed in greater detail below, with reference to FIG. 3.

In a further aspect, balloons 102A to 102F may utilize one or more ofvarious different RF air-interface protocols for communication withground-based stations 106 via respective RF links 108. For instance,some or all of balloons 102A to 102F may be configured to communicatewith ground-based stations 106 using protocols described in IEEE 802.11(including any of the IEEE 802.11 revisions), various cellular protocolssuch as GSM, CDMA, UMTS, EV-DO, WiMAX, and/or LTE, and/or one or morepropriety protocols developed for balloon-ground RF communication, amongother possibilities.

In a further aspect, there may scenarios where RF links 108 do notprovide a desired link capacity for balloon-ground communications. Forinstance, increased capacity may be desirable to provide backhaul linksfrom a ground-based gateway, and in other scenarios as well.Accordingly, an exemplary network may also include downlink balloons,which provide a high-capacity air-ground link.

For example, in balloon network 100, balloon 102F is configured as adownlink balloon. Like other balloons in an exemplary network, adownlink balloon 102F may be operable for optical communication withother balloons via optical links 104. However, a downlink balloon 102Fmay also be configured for free-space optical communication with aground-based station 112 via an optical link 110. Optical link 110 maytherefore serve as a high-capacity link (as compared to an RF link 108)between the balloon network 100 and a ground-based station 108.

Note that in some implementations, a downlink balloon 102F mayadditionally be operable for RF communication with ground-based stations106. In other cases, a downlink balloon 102F may only use an opticallink for balloon-to-ground communications. Further, while thearrangement shown in FIG. 1 includes just one downlink balloon 102F, anexemplary balloon network can also include multiple downlink balloons.On the other hand, a balloon network can also be implemented without anydownlink balloons.

In other implementations, a downlink balloon may be equipped with aspecialized, high-bandwidth RF communication system forballoon-to-ground communications, instead of, or in addition to, afree-space optical communication system. The high-bandwidth RFcommunication system may take the form of an ultra-wideband system,which may provide an RF link with substantially the same capacity as oneof the optical links 104. Other forms are also possible.

Ground-based stations, such as ground-based stations 106 and/or 108, maytake various forms. Generally, a ground-based station may includecomponents such as transceivers, transmitters, and/or receivers forcommunication via RF links and/or optical links with a balloon network.Further, a ground-based station may use various air-interface protocolsin order to communicate with a balloon 102A to 102F over an RF link. Assuch, a ground-based station 106 may be configured as an access pointvia which various devices can connect to balloon network 100.Ground-based stations 106 may have other configurations and/or serveother purposes without departing from the scope of the invention.

In a further aspect, some or all balloons 102A to 102F could beconfigured to establish a communication link with space-based satellitesin addition to, or as an alternative to, a ground-based communicationlink. In some embodiments, a balloon may communicate with a satellitevia an optical link. However, other types of satellite communicationsare also possible.

Further, some ground-based stations, such as ground-based station 108,may be configured as gateways between balloon network 100 and one ormore other networks. Such a ground-based station 108 may thus serve asan interface between the balloon network and the Internet, a cellularservice provider's network, and/or other types of networks. Variationson this configuration and other configurations of a ground-based station108 are also possible.

A. Mesh-Network Functionality

As noted, balloons 102A to 102F may collectively function as a meshnetwork. More specifically, since balloons 102A to 102F may communicatewith one another using free-space optical links, the balloons maycollectively function as a free-space optical mesh network.

In a mesh-network configuration, each balloon 102A to 102F may functionas a node of the mesh network, which is operable to receive datadirected to it and to route data to other balloons. As such, data may berouted from a source balloon to a destination balloon by determining anappropriate sequence of optical links between the source balloon and thedestination balloon. These optical links may be collectively referred toas a “lightpath” for the connection between the source and destinationballoons. Further, each of the optical links may be referred to as a“hop” on the lightpath.

To operate as a mesh network, balloons 102A to 102F may employ variousrouting techniques and self-healing algorithms. In some embodiments, aballoon network 100 may employ adaptive or dynamic routing, where alightpath between a source and destination balloon is determined andset-up when the connection is needed, and released at a later time.Further, when adaptive routing is used, the lightpath may be determineddynamically depending upon the current state, past state, and/orpredicted state of the balloon network.

In addition, the network topology may change as the balloons 102A to102F move relative to one another and/or relative to the ground.Accordingly, an exemplary balloon network 100 may apply a mesh protocolto update the state of the network as the topology of the networkchanges. For example, to address the mobility of the balloons 102A to102F, balloon network 100 may employ and/or adapt various techniquesthat are employed in mobile ad hoc networks (MANETs). Other examples arepossible as well.

In some implementations, a balloon network 100 may be configured as atransparent mesh network. More specifically, in a transparent balloonnetwork, the balloons may include components for physical switching thatis entirely optical, without any electrical components involved in thephysical routing of optical signals. Thus, in a transparentconfiguration with optical switching, signals travel through a multi-hoplightpath that is entirely optical.

In other implementations, the balloon network 100 may implement afree-space optical mesh network that is opaque. In an opaqueconfiguration, some or all balloons 102A to 102F may implementoptical-electrical-optical (OEO) switching. For example, some or allballoons may include optical cross-connects (OXCs) for OEO conversion ofoptical signals. Other opaque configurations are also possible.

In a further aspect, balloons in an exemplary balloon network 100 mayimplement wavelength division multiplexing (WDM), which may help toincrease link capacity. When WDM is implemented with transparentswitching, physical lightpaths through the balloon network may besubject to the “wavelength continuity constraint.” More specifically,because the switching in a transparent network is entirely optical, itmay be necessary to assign the same wavelength for all optical links ona given lightpath.

An opaque configuration, on the other hand, may avoid the wavelengthcontinuity constraint. In particular, balloons in an opaque balloonnetwork may include the OEO switching systems operable for wavelengthconversion. As a result, balloons can convert the wavelength of anoptical signal at each hop along a lightpath.

Further, various routing algorithms may be employed in an opaqueconfiguration. For example, to determine a primary lightpath and/or oneor more diverse backup lightpaths for a given connection, exemplaryballoons may apply or consider shortest-path routing techniques such asDijkstra's algorithm and k-shortest path, and/or edge and node-diverseor disjoint routing such as Suurballe's algorithm, among others.Additionally or alternatively, techniques for maintaining a particularquality of service (QoS) may be employed when determining a lightpath.Other techniques are also possible.

B. Station-Keeping Functionality

In an exemplary embodiment, a balloon network 100 may implementstation-keeping functions to help provide a desired network topology.For example, station-keeping may involve each balloon 102A to 102Fmaintaining and/or moving into a certain position relative to one ormore other balloons in the network (and possibly in a certain positionrelative to the ground). As part of this process, each balloon 102A to102F may implement station-keeping functions to determine its desiredpositioning within the desired topology, and if necessary, to determinehow to move to the desired position.

The desired topology may vary depending upon the particularimplementation. In some cases, balloons may implement station-keeping toprovide a substantially uniform topology. In such cases, a given balloon102A to 102F may implement station-keeping functions to position itselfat substantially the same distance (or within a certain range ofdistances) from adjacent balloons in the balloon network 100.

In other cases, a balloon network 100 may have a non-uniform topology.For instance, exemplary embodiments may involve topologies whereballoons are distributed more or less densely in certain areas, forvarious reasons. As an example, to help meet the higher bandwidthdemands that are typical in urban areas, balloons may be clustered moredensely over urban areas. For similar reasons, the distribution ofballoons may be denser over land than over large bodies of water. Manyother examples of non-uniform topologies are possible.

In a further aspect, the topology of an exemplary balloon network may beadaptable. In particular, station-keeping functionality of exemplaryballoons may allow the balloons to adjust their respective positioningin accordance with a change in the desired topology of the network. Forexample, one or more balloons could move to new positions to increase ordecrease the density of balloons in a given area. Other examples arepossible.

In some embodiments, a balloon network 100 may employ an energy functionto determine if and/or how balloons should move to provide a desiredtopology. In particular, the state of a given balloon and the states ofsome or all nearby balloons may be input to an energy function. Theenergy function may apply the current states of the given balloon andthe nearby balloons to a desired network state (e.g., a statecorresponding to the desired topology). A vector indicating a desiredmovement of the given balloon may then be determined by determining thegradient of the energy function. The given balloon may then determineappropriate actions to take in order to effectuate the desired movement.For example, a balloon may determine an altitude adjustment oradjustments such that winds will move the balloon in the desired manner.

C. Control of Balloons in a Balloon Network

In some embodiments, mesh networking and/or station-keeping functionsmay be centralized. For example, FIG. 2 is a block diagram illustratinga balloon-network control system, according to an exemplary embodiment.In particular, FIG. 2 shows a distributed control system, which includesa central control system 200 and a number of regional control-systems202A to 202B. Such a control system may be configured to coordinatecertain functionality for balloon network 204, and as such, may beconfigured to control and/or coordinate certain functions for balloons206A to 206I.

In the illustrated embodiment, central control system 200 may beconfigured to communicate with balloons 206A to 206I via a number ofregional control systems 202A to 202C. These regional control systems202A to 202C may be configured to receive communications and/oraggregate data from balloons in the respective geographic areas thatthey cover, and to relay the communications and/or data to centralcontrol system 200. Further, regional control systems 202A to 202C maybe configured to route communications from central control system 200 tothe balloons in their respective geographic areas. For instance, asshown in FIG. 2, regional control system 202A may relay communicationsand/or data between balloons 206A to 206C and central control system200, regional control system 202B may relay communications and/or databetween balloons 206D to 206F and central control system 200, andregional control system 202C may relay communications and/or databetween balloons 206G to 206I and central control system 200.

In order to facilitate communications between the central control system200 and balloons 206A to 206I, certain balloons may be configured asdownlink balloons, which are operable to communicate with regionalcontrol systems 202A to 202C. Accordingly, each regional control system202A to 202C may be configured to communicate with the downlink balloonor balloons in the respective geographic area it covers. For example, inthe illustrated embodiment, balloons 204A, 204D, and 204H are configuredas downlink balloons. As such, regional control systems 202A to 202C mayrespectively communicate with balloons 204A, 204D, and 204H via opticallinks 206, 208, and 210, respectively.

In the illustrated configuration, only some of balloons 206A to 206I areconfigured as downlink balloons. The balloons 206A, 206F, and 206I thatare configured as downlink balloons may relay communications fromcentral control system 200 to other balloons in the balloon network,such as balloons 206B-E and 206G-H. However, it should be understoodthat it in some implementations, it is possible that all balloons mayfunction as downlink balloons. Further, while FIG. 2 shows multipleballoons configured as downlink balloons, it is also possible for aballoon network to include only one downlink balloon, or possibly evenno downlink balloons.

Note that a regional control system 202A to 202B may in fact just be aparticular type of ground-based station that is configured tocommunicate with downlink balloons (e.g., such as ground-based station112 of FIG. 1). Thus, while not shown in FIG. 2, a control system may beimplemented in conjunction with other types of ground-based stations(e.g., access points, gateways, etc.).

In a centralized control arrangement, such as that shown in FIG. 2, thecentral control system 200 (and possibly regional control systems 202Ato 202C as well) may coordinate certain mesh-networking functions forballoon network 204. For example, balloons 206A to 206I may send thecentral control system 200 certain state information, which the centralcontrol system 200 may utilize to determine the state of balloon network204. The state information from a given balloon may include locationdata, optical-link information (e.g., the identity of other balloonswith which the balloon has established an optical link, the bandwidth ofthe link, wavelength usage and/or availability on a link, etc.), winddata collected by the balloon, and/or other types of information.Accordingly, the central control system 200 may aggregate stateinformation from some or all of the balloons 206A to 206I in order todetermine an overall state of the network.

The overall state of the network may then be used to coordinate and/orfacilitate certain mesh-networking functions such as determininglightpaths for connections. For example, the central control system 200may determine a current topology based on the aggregate stateinformation from some or all of the balloons 206A to 206I. The topologymay provide a picture of the current optical links that are available inballoon network and/or the wavelength availability on the links. Thistopology may then be sent to some or all of the balloons so that arouting technique may be employed to select appropriate lightpaths (andpossibly backup lightpaths) for communications through the balloonnetwork 204.

In a further aspect, the central control system 200 (and possiblyregional control systems 202A to 202C as well) may also coordinatecertain station-keeping functions for balloon network 204. For example,the central control system 200 may input state information that isreceived from balloons 206A to 206I to an energy function, which mayeffectively compare the current topology of the network to a desiredtopology, and provide a vector indicating a direction of movement (ifany) for each balloon, such that the balloons can move towards thedesired topology. Further, the central control system 200 may usealtitudinal wind data to determine respective altitude adjustments thatmay be initiated to achieve the movement towards the desired topology.The central control system 200 may provide and/or support otherstation-keeping functions as well.

FIG. 2 shows a distributed arrangement that provides centralizedcontrol, with regional control systems 202A to 202C coordinatingcommunications between a central control system 200 and a balloonnetwork 204. Such an arrangement may be useful to provide centralizedcontrol for a balloon network that covers a large geographic area. Insome embodiments, a distributed arrangement may even support a globalballoon network that provides coverage everywhere on earth. Of course, adistributed-control arrangement may be useful in other scenarios aswell.

Further, it should be understood that other control-system arrangementsare also possible. For instance, some implementations may involve acentralized control system with additional layers (e.g., sub-regionsystems within the regional control systems, and so on). Alternatively,control functions may be provided by a single, centralized, controlsystem, which communicates directly with one or more downlink balloons.

In some embodiments, control and coordination of a balloon network maybe shared by a ground-based control system and a balloon network tovarying degrees, depending upon the implementation. In fact, in someembodiments, there may be no ground-based control systems. In such anembodiment, all network control and coordination functions may beimplemented by the balloon network itself. For example, certain balloonsmay be configured to provide the same or similar functions as centralcontrol system 200 and/or regional control systems 202A to 202C. Otherexamples are also possible.

Furthermore, control and/or coordination of a balloon network may bede-centralized. For example, each balloon may relay state informationto, and receive state information from, some or all nearby balloons.Further, each balloon may relay state information that it receives froma nearby balloon to some or all nearby balloons. When all balloons doso, each balloon may be able to individually determine the state of thenetwork. Alternatively, certain balloons may be designated to aggregatestate information for a given portion of the network. These balloons maythen coordinate with one another to determine the overall state of thenetwork.

Further, in some aspects, control of a balloon network may be partiallyor entirely localized, such that it is not dependent on the overallstate of the network. For example, individual balloons may implementstation-keeping functions that only consider nearby balloons. Inparticular, each balloon may implement an energy function that takesinto account its own state and the states of nearby balloons. The energyfunction may be used to maintain and/or move to a desired position withrespect to the nearby balloons, without necessarily considering thedesired topology of the network as a whole. However, when each balloonimplements such an energy function for station-keeping, the balloonnetwork as a whole may maintain and/or move towards the desiredtopology.

As an example, each balloon A may receive distance information d₁ tod_(k) with respect to each of its k closest neighbors. Each balloon Amay treat the distance to each of the k balloons as a virtual springwith vector representing a force direction from the first nearestneighbor balloon i toward balloon A and with force magnitudeproportional to d_(i). The balloon A may sum each of the k vectors andthe summed vector is the vector of desired movement for balloon A.Balloon A may attempt to achieve the desired movement by controlling itsaltitude.

Alternatively, this process could assign the force magnitude of each ofthese virtual forces equal to d_(i)×d_(i), for instance. Otheralgorithms for assigning force magnitudes for respective balloons in amesh network are possible.

In another embodiment, a similar process could be carried out for eachof the k balloons and each balloon could transmit its planned movementvector to its local neighbors. Further rounds of refinement to eachballoon's planned movement vector can be made based on the correspondingplanned movement vectors of its neighbors. It will be evident to thoseskilled in the art that other algorithms could be implemented in aballoon network in an effort to maintain a set of balloon spacingsand/or a specific network capacity level over a given geographiclocation.

D. Exemplary Balloon Configuration

Various types of balloon systems may be incorporated in an exemplaryballoon network. As noted above, an exemplary embodiment may utilizehigh-altitude balloons, which typically operate in an altitude rangebetween 18 km and 22 km. FIG. 3 shows a high-altitude balloon 300,according to an exemplary embodiment. As shown, the balloon 300 includesan envelope 302, a skirt 304, a payload 306, and a cut-down system 308that is attached between the balloon 302 and payload 304.

The envelope 302 and skirt 304 may take various forms, which may becurrently well-known or yet to be developed. For instance, the envelope302 and/or skirt 304 may be made of metalized Mylar or BoPet.Alternatively or additionally, some or all of the envelope 302 and/orskirt 304 may be constructed from a highly-flexible latex material or arubber material such as chloroprene. Other materials are also possible.Further, the shape and size of the envelope 302 and skirt 304 may varydepending upon the particular implementation. Additionally, the envelope302 may be filled with various different types of gases, such as heliumand/or hydrogen. Other types of gases are possible as well.

The payload 306 of balloon 300 may include a processor 312 and on-boarddata storage, such as memory 314. The memory 314 may take the form of orinclude a non-transitory computer-readable medium. The non-transitorycomputer-readable medium may have instructions stored thereon, which canbe accessed and executed by the processor 312 in order to carry out theballoon functions described herein.

The payload 306 of balloon 300 may also include various other types ofequipment and systems to provide a number of different functions. Forexample, payload 306 may include optical communication system 316, whichmay transmit optical signals via an ultra-bright LED system 320, andwhich may receive optical signals via an optical-communication receiver(e.g., a photo-diode receiver system). Further, payload 306 may includean RF communication system 318, which may transmit and/or receive RFcommunications via an antenna system 324.

The payload 306 may also include a power supply 326 to supply power tothe various components of balloon 300. The power supply 326 may includeor take the form of a rechargeable battery. In other embodiments, thepower supply 326 may additionally or alternatively represent other meansknown in the art for producing power. In addition, the balloon 300 mayinclude a solar power generation system 327. The solar power generationsystem 327 may include solar panels and could be used to generate powerthat charges and/or is distributed by the power supply 326.

Further, payload 306 may include various types of other systems andsensors 328. For example, payload 306 may include one or more videoand/or still cameras, a GPS system, various motion sensors (e.g.,accelerometers, gyroscopes, and/or compasses), and/or various sensorsfor capturing environmental data. Further, some or all of the componentswithin payload 306 may be implemented in a radiosonde, which may beoperable to measure, e.g., pressure, altitude, geographical position(latitude and longitude), temperature, relative humidity, and/or windspeed and/or direction, among other information.

As noted, balloon 306 includes an ultra-bright LED system 320 forfree-space optical communication with other balloons. As such, opticalcommunication system 316 may be configured to transmit a free-spaceoptical signal by modulating the ultra-bright LED system 320. Theoptical communication system 316 may be implemented with mechanicalsystems and/or with hardware, firmware, and/or software. Generally, themanner in which an optical communication system is implemented may vary,depending upon the particular application.

In a further aspect, balloon 300 may be configured for altitude control.For instance, balloon 300 may include a variable buoyancy system, whichis configured to change the altitude of the balloon 300 by adjusting thevolume and/or density of the gas in the balloon 300. A variable buoyancysystem may take various forms, and may generally be any system that canchange the volume and/or density of gas in envelope 302.

In an exemplary embodiment, a variable buoyancy system may include abladder 310 that is located inside of envelope 302. The bladder 310could be an elastic chamber configured to hold liquid and/or gas.Alternatively, the bladder 310 need not be inside the envelope 302. Forinstance, the bladder 310 could be a rigid bladder that could bepressurized well beyond neutral pressure. The buoyancy of the balloon300 may therefore be adjusted by changing the density and/or volume ofthe gas in bladder 310. To change the density in bladder 310, balloon300 may be configured with systems and/or mechanisms for heating and/orcooling the gas in bladder 310. Further, to change the volume, balloon300 may include pumps or other features for adding gas to and/orremoving gas from bladder 310. Additionally or alternatively, to changethe volume of bladder 310, balloon 300 may include release valves orother features that are controllable to allow gas to escape from bladder310. Multiple bladders 310 could be implemented within the scope of thisdisclosure. For instance, multiple bladders could be used to improveballoon stability.

In an example embodiment, the envelope 302 could be filled with helium,hydrogen or other lighter-than-air material. The envelope 302 could thushave an associated upward buoyancy force. In such an embodiment, air inthe bladder 310 could be considered a ballast tank that may have anassociated downward ballast force. In another example embodiment, theamount of air in the bladder 310 could be changed by pumping air (e.g.,with an air compressor) into and out of the bladder 310. By adjustingthe amount of air in the bladder 310, the ballast force may becontrolled. In some embodiments, the ballast force may be used, in part,to counteract the buoyancy force and/or to provide altitude stability.

In other embodiments, the envelope 302 could be substantially rigid andinclude an enclosed volume. Air could be evacuated from envelope 302while the enclosed volume is substantially maintained. In other words,at least a partial vacuum could be created and maintained within theenclosed volume. Thus, the envelope 302 and the enclosed volume couldbecome lighter than air and provide a buoyancy force. In yet otherembodiments, air or another material could be controllably introducedinto the partial vacuum of the enclosed volume in an effort to adjustthe overall buoyancy force and/or to provide altitude control.

In another embodiment, a portion of the envelope 302 could be a firstcolor (e.g., black) and/or a first material from the rest of envelope302, which may have a second color (e.g., white) and/or a secondmaterial. For instance, the first color and/or first material could beconfigured to absorb a relatively larger amount of solar energy than thesecond color and/or second material. Thus, rotating the balloon suchthat the first material is facing the sun may act to heat the envelope302 as well as the gas inside the envelope 302. In this way, thebuoyancy force of the envelope 302 may increase. By rotating the balloonsuch that the second material is facing the sun, the temperature of gasinside the envelope 302 may decrease. Accordingly, the buoyancy forcemay decrease. In this manner, the buoyancy force of the balloon could beadjusted by changing the temperature/volume of gas inside the envelope302 using solar energy. In such embodiments, it is possible that abladder 310 may not be a necessary element of balloon 300. Thus, variouscontemplated embodiments, altitude control of balloon 300 could beachieved, at least in part, by adjusting the rotation of the balloonwith respect to the sun.

Further, a balloon 306 may include a navigation system (not shown). Thenavigation system may implement station-keeping functions to maintainposition within and/or move to a position in accordance with a desiredtopology. In particular, the navigation system may use altitudinal winddata to determine altitudinal adjustments that result in the windcarrying the balloon in a desired direction and/or to a desiredlocation. The altitude-control system may then make adjustments thedensity of the balloon chamber in order to effectuate the determinedaltitudinal adjustments and cause the balloon to move laterally to thedesired direction and/or to the desired location.

Alternatively, the altitudinal adjustments may be computed by aground-based control system and communicated to the high-altitudeballoon. As another alternative, the altitudinal adjustments may becomputed by a ground-based or satellite-based control system andcommunicated to the high-altitude balloon. Furthermore, in someembodiments, specific balloons in a heterogeneous balloon network may beconfigured to compute altitudinal adjustments for other balloons andtransmit the adjustment commands to those other balloons.

As shown, the balloon 300 also includes a cut-down system 308. Thecut-down system 308 may be activated to separate the payload 306 fromthe rest of balloon 300. This functionality may be utilized anytime thepayload needs to be accessed on the ground, such as when it is time toremove balloon 300 from a balloon network, when maintenance is due onsystems within payload 306, and/or when power supply 326 needs to berecharged or replaced.

In an exemplary embodiment, the cut-down system 308 may include aconnector, such as a balloon cord, connecting the payload 306 to theenvelope 302 and a means for severing the connector (e.g., a shearingmechanism or an explosive bolt). In an example embodiment, the ballooncord, which may be nylon, is wrapped with a nichrome wire. A currentcould be passed through the nichrome wire to heat it and melt the cord,cutting the payload 306 away from the envelope 302. Other types ofcut-down systems and/or variations on the illustrated cut-down system308 are possible as well.

In an alternative arrangement, a balloon may not include a cut-downsystem. In such an arrangement, the navigation system may be operable tonavigate the balloon to a landing location, in the event the balloonneeds to be removed from the network and/or accessed on the ground.Further, it is possible that a balloon may be self-sustaining, such thatit theoretically does not need to be accessed on the ground. In yetother embodiments, balloons may be serviced in-flight by specificservice balloons or another type of service aerostat or serviceaircraft.

III. Balloon Network with Optical and RF Links Between Balloons

In some embodiments, a high-altitude-balloon network may includesuper-node balloons, which communicate with one another via opticallinks, as well as sub-node balloons, which communicate with super-nodeballoons via RF links. FIG. 4 is a simplified block diagram illustratinga balloon network that includes super-nodes and sub-nodes, according toan exemplary embodiment. More specifically, FIG. 4 illustrates a portionof a balloon network 400 that includes super-node balloons 410A to 410C(which may also be referred to as “super-nodes”) and sub-node balloons420A to 420Q (which may also be referred to as “sub-nodes”).

Each super-node balloon 410A to 410C may include a free-space opticalcommunication system that is operable for packet-data communication withother super-node balloons. As such, super-nodes may communicate with oneanother over optical links. For example, in the illustrated embodiment,super-node 410A and super-node 401B may communicate with one anotherover optical link 402, and super-node 410A and super-node 401C maycommunicate with one another over optical link 404.

Each of the sub-node balloons 420A to 420Q may include a radio-frequency(RF) communication system that is operable for packet-data communicationover one or more RF air interfaces. Accordingly, some or all of thesuper-node balloons 410A to 410C may include an RF communication systemthat is operable to route packet data to one or more nearby sub-nodeballoons 420A to 420Q. When a sub-node 420A receives data from asuper-node 410A via an RF link, the sub-node 420A may in turn use its RFcommunication system to transmit the received data to a ground-basedstation 430A to 430L via an RF link.

In some embodiments, all sub-node balloons may be configured toestablish RF links with ground-based stations. For example, allsub-nodes may be configured similarly to sub-node 420A, which isoperable to relay communications between super-node 410A and aground-based station 430A via respective RF links.

In other embodiments, some or all sub-nodes may also be configured toestablish RF links with other sub-nodes. For instance, in theillustrated embodiment, sub-node balloon 420F is operable to relaycommunications between super-node 410C and sub-node balloon 420E. Insuch an embodiment, two or more sub-nodes may provide a multi-hop pathbetween a super-node balloon and a ground-based station, such as themulti-hop path provided between super-node 410C and a ground-basedstation 430E by sub-node balloons 420E and 420F.

Note that an RF link may be a directional link between a given entityand one or more other entities, or may be part of an omni-directionalbroadcast. In the case of an RF broadcast, it is possible that one ormore “links” may be provided via a single broadcast. For example,super-node balloon 410A may establish a separate RF link with each ofsub-node balloons 420A, 420B, and 420C. However, in otherimplementations, super-node balloon 410A may broadcast a single RFsignal that can be received by sub-node balloons 420A, 420B, and 420C.In such an implementation, the single RF broadcast may effectivelyprovide all of the RF links between super-node balloon 410A and sub-nodeballoons 420A, 420B, and 420C. Other examples are also possible.

Generally, the free-space optical links between super-node balloons havemore bandwidth capacity than the RF links between super-node balloonsand sub-node balloons. Further, free-space optical communication may bereceived at a much greater distance than RF communications. As such, thesuper-node balloons 410A to 410C may function as the backbone of theballoon network 400, while the sub-nodes 420A to 420Q may providesub-networks providing access to the balloon network and/or connectingthe balloon network to other networks.

As noted above, the super-nodes 410A to 410C may be configured for bothlonger-range optical communication with other super-nodes andshorter-range RF communications with nearby sub-nodes 420. For example,super-nodes 410A to 410C may use high-power or ultra-bright LEDs totransmit optical signals over optical links 402, 404, which may extendfor as much as 100 miles, or possibly more. Configured as such, thesuper-nodes 410A to 410C may be capable of optical communications atdata rates of 10 to 50 Gbit/sec.

A larger number of high-altitude balloons may then be configured assub-nodes, which may communicate with ground-based Internet nodes atdata rates on the order of approximately 10 Mbit/sec. For instance, inthe illustrated implementation, the sub-nodes 420A to 420Q may beconfigured to connect the super-nodes 410A to 410C to other networksand/or directly to client devices. Note that the data rates and linkdistances described in the above example and elsewhere herein areprovided for illustrative purposes and should not be consideredlimiting; other data rates and link distances are possible.

In a further aspect, some or all of the super-node balloons may beconfigured as downlink balloons. Additionally or alternatively, some orall of sub-nodes 420A to 420Q may be configured as downlink balloons.Further, it is possible that a hierarchical balloon network such as thatshown in FIG. 4 may be implemented without any downlink balloons.

Further, in some embodiments, the super-node balloons, such assuper-nodes 410A to 410C, may function as a core network (i.e., abackbone network), while the sub-node balloons 420A to 420Q may functionas one or more access networks to the core network of super-nodes. Insuch an embodiment, some or all of the sub-nodes 420A to 420Q may alsofunction as gateways to the balloon network 400. Note also that in someembodiments, some or all of the ground-based stations 430A to 430L mayadditionally or alternatively function as gateways to balloon network400.

In another aspect, it should be understood that the network topology ofthe hierarchical balloon network shown in FIG. 4 is but one of manypossible network topologies. Further, the network topology of anexemplary balloon network may vary dynamically as super-node and/orsub-node balloons move relative to the ground and/or relative to oneanother. Further, as with the balloon networks illustrated in FIGS. 1and 2, a desired topology may be specified for a hierarchical balloonnetwork may change dynamically over time as service needs and/or goalsof the network change.

A. Station-Keeping in an Exemplary Hierarchical Balloon Network

In a further aspect, station-keeping functionality may be employed by anexemplary balloon network in order to achieve a topology that conformswith or that deviates by an acceptable amount from the desired topology.Thus, while station-keeping functionality may be implemented with thetheoretical goal of achieving the desired topology, exemplarystation-keeping functionality may also be implemented in accordance withflexible station-keeping parameters, rather than rigid rules as to thepositioning of the balloons relative to the ground and/or relative toeach other. For example, station-keeping parameters in a balloon networkmay include ranges of acceptable distances separating balloons and/oracceptable variation from desired (i.e., target) densities of balloons.Other station-keeping parameters are possible as well.

Allowing such deviation from the desired topology may be particularlyuseful when balloons rely solely on altitude control in order to controlmovement (e.g., by moving to an altitude where the wind carries theballoon towards a desired location). More specifically, in this flexibleframework, the super-nodes and or sub-nodes may move relative to oneanother while staying substantially within the constraints of thedesired topology. In particular, since exemplary high-altitude balloonsmay have no other means for horizontal movement other than windscarrying the balloons, the balloons may be in substantially continualmovement. As such, the balloons may evaluate altitudinal wind data, aswell as their own position and positions of nearby balloons. Theballoons may then apply an energy function to this data to determine adirection of movement that is desired, and then adjust altitude (ifnecessary) to help achieve movement in the desired direction. Of course,other techniques for determining a desired direction are also possible.

In a further aspect, when a number of balloons are located in a certainarea, and one or more of the balloons is substantially unused (or beingused at a lower level than is desirable), the balloons in the area maycoordinate to have one or more of the balloons depart from the area. Inparticular, the selected balloon or balloons may change altitude inorder to reach a faster-moving layer of air than the other balloons inthe area. A selected balloon may therefore move more quickly than theother balloons in the area, until it reaches another area in the balloonnetwork. When a selected balloon reaches the other area, it may thenadjust altitude so as to move into a layer of air having the same orsimilar wind speed as other balloons in the area that it has moved into.By undergoing this process, balloons may effectively move from one partof the network to another. As such, this process may be used to shiftnetwork resources, e.g., from areas where bandwidth is being underutilized to areas where more bandwidth is desirable.

FIGS. 5A and 5B show an area 501 covered by a portion of a balloonnetwork 500, according to an exemplary embodiment. In the state ofballoon network 500 that is shown in FIG. 5A, the desired topology mayspecify that the balloon network 500 should preferably have a certaindensity (i.e., a certain number of super-nodes and/or a certain numberof sub-nodes) and should preferably be distributed evenly (e.g., suchthat the balloons are equidistant from one another) within the area 502.In the framework of these station-keeping parameters, super-nodeballoons 510A to 510C and sub-node balloons 520A to 520I may be locatedover the geographic area 501, as shown in FIG. 5A.

However, since the balloons in balloon network 500 may be insubstantially continual motion, it should be understood that FIG. 5A mayrepresent a momentary state of the balloon network 500. Thus, thetopology of the balloon network 500 may look very different at a laterpoint in time, while still conforming with the same station-keepingparameters and the same desired topology. For example, in the state ofballoon network 500 shown in FIG. 5B, the positions of the super-nodeballoons 510A to 510C and the sub-node balloons 520A to 520I havechanged relative to the ground and relative to one another, as comparedto the positions shown in FIG. 5A.

The change in network state shown between FIGS. 5A and 5B alsoillustrates how the balloon network may set-up and take down opticallinks and/or RF links as the balloons move within the framework definedby a set of station-keeping parameters. More specifically, in FIG. 5A,there is an optical link between super-node balloons 510A and 510B,between super-node balloons 510A and 510C, and between super-nodeballoons 510B and 510C. However, in FIG. 5B, super-node 510C has movedout of geographic area 501 such that it is no longer positioned withinthe acceptable distance range from super-nodes 510A and 510B. Further,another super-node balloon 510D has moved into geographic area 501, to aposition that is within the acceptable distance range from super-nodes510A and 510B. Accordingly, in the network state shown in FIG. 5B, theoptical link between super-node balloons 510A and 510C and the opticallink between super-node balloons 510B and 510C have been taken down.Further, in the state illustrated in FIG. 5B, super-node balloons 510Cand 510D are within an acceptable distance from one another and as such,an optical link has been set up between super-node balloons 510C and510D.

As further shown in FIG. 5B, the positioning of each sub-node balloon520A to 520I has changed relative to the super-node balloons 510A to510C and the other sub-node balloons. More specifically, in the stateshown in FIG. 5A, super-node balloon 510A has established RF links withsub-nodes 520A, 520B, and 520C, super-node balloon 510B has establishedRF links with sub-nodes 520D, 520E, and 520F, and super-node balloon510C has established RF links with sub-nodes 520G, 520H, and 520I.However, in the network state shown in FIG. 5B, super-node balloon 510Ahas only maintained the RF link with sub-node 520B, and has establishednew RF links with sub-nodes 520D and 520H. Further, super-node balloon510B has only maintained the RF link with sub-node 520E, and hasestablished new RF links with sub-nodes 520A and 520G.

Yet further, super-node balloon 510C no longer has RF links with any ofthe sub-nodes 520A to 520I. Instead, super-node balloon 510D hasestablished RF links with sub-nodes 520C, 520F, and 520I. Note, however,that super-node balloon 510C may have established a new RF link or linkswith other sub-nodes, which are not shown in FIG. 5B.

In a further aspect, FIGS. 5A and 5B also illustrate the fact thatballoons may be interchangeable for purposes of station-keeping. Morespecifically, in FIG. 5B, super-node balloon 510C has moved such thatthe distance between super-node 510C and super-nodes 510A and 510B isbeyond the upper extent of the acceptable distance range specified bycurrent station-keeping parameters. However, exemplary station-keepingfunctionality may allow this to occur for various reasons. For example,station-keeping parameters may also specify a desired density ofsuper-node balloons (e.g., the number of super-node balloons that isdesirable in a certain area). In the illustrated example, a super-nodedensity parameter may specify that three super-nodes should generally belocated within area 501. Accordingly, if super-node 510D moves into area501, another super-node (e.g., super-node 510C) may be allowed to moveout of area 501. Other examples are also possible.

In a further aspect of some implementations, a desired topology for ahierarchical balloon network may be may be defined withoutdifferentiating between super-node balloons and sub-node balloons. Insuch an embodiment, station-keeping may be implemented in the same or ina similar manner by super-nodes 510A to 510D and sub-nodes 520A to 520I.For example, the desired topology may define a certain desired distancebetween adjacent balloons. As such, the desired distance between asuper-node and another super-node may be the same as the desireddistance between a super-node and a sub-node, and the same as thedesired distance between two sub-nodes. Other examples of such anon-differentiated desired topology and/or of such uniformstation-keeping are also possible.

When the desired topology does not differentiate between super-nodeballoons and sub-node balloons, the super-node balloons may additionallybe configured to function as sub-nodes. In particular, the super-nodeballoons may be operable to establish and communicate via RF links withground-based stations, as well as via optical links with othersuper-nodes and RF links with other sub-nodes. As such, the networkcoverage provided by a super-node and sub-node may be equivalent fromthe perspective of ground-based stations, which may be desirable when ina non-differentiated topology, where super-nodes and sub-nodes areessentially interchangeable within the topology. Note also that some orall super-nodes may be dually configured as sub-nodes in otherembodiments, in which the desired topology may or may not benon-differentiated.

In some implementations, the spacing of adjacent super-nodes may differfrom the desired spacing of adjacent sub-nodes and/or the desiredspacing between a super-node and an adjacent sub-node. For example,consider an embodiment where the super-node balloons 510A to 510Dfunction as the backbone network, and where the sub-node balloonsfunction as one or more access networks. In such an embodiment,station-keeping parameters for the sub-nodes 520A to 520I may specify anacceptable distance range for adjacent sub-nodes. In an exemplaryimplementation, this distance range may be selected so as to helpprovide substantially continuous coverage in a given geographic area501. However, distance ranges may be selected for other purposes aswell.

Further, station-keeping parameters for super-node balloons, such assuper-nodes 510A to 510D, may include a desired distance betweenadjacent super-nodes. When the super-nodes form a backbone network, thedistance between adjacent super-nodes may be substantially greater thanbetween super-nodes and adjacent sub-nodes and between adjacentsub-nodes. In practice, the acceptable distance range may extend to therange of the free-space optical communications systems employed by thesuper-nodes. In some cases, however, the acceptable distance rangebetween super-nodes may be defined in view of other goals, such asincreasing bandwidth in certain areas (e.g., by decreasing the upperextent of the acceptable distance range and thus increasing thedensity).

Yet further, the desired topology may include a separately defineddesired distance between super-node balloons and adjacent sub-nodeballoons. As such, station-keeping parameters for super-nodes and/or forsub-nodes may include an acceptable distance range between super-nodesand adjacent sub-nodes.

When a hierarchical balloon network implements such station-keepingfunctionality, the super-nodes may move in an effort to positionthemselves within the defined distance range from adjacent super-nodes,while at the same time positioning themselves within the defineddistance range from adjacent sub-nodes. Additionally, the sub-nodes maymove in an effort to position themselves within the defined distancerange from adjacent sub-nodes, and also within the defined distancerange. In such an embodiment, the super-nodes implement station-keepingfunctionality to establish and/or maintain the positioning of thesuper-nodes relative to the sub-nodes (e.g., of keeping the distancebetween super-nodes and adjacent sub-nodes within the acceptable range).

In other embodiments, super-nodes and sub-nodes may share theresponsibility of keeping the distances between super-nodes and adjacentsub-nodes within the acceptable range. Further, in yet otherembodiments, the sub-nodes may implement station-keeping functionalityto establish and/or maintain the positioning of the super-nodes relativeto the sub-nodes. In either case, the sub-nodes may move in an effort toposition themselves within the acceptable distance range to adjacentsuper-nodes, while at the same time positioning themselves within theacceptable distance range to adjacent sub-nodes.

B. Geographically-Defined Station-Keeping

As noted above, station-keeping parameters for an exemplary balloonnetwork 500 may specify a general geographic area 501 in which certainacceptable distances and/or spacing between balloons should apply.Further, exemplary station-keeping parameters may be defined separatelyfor each of a number of such areas. Each such area may therefore havedifferent acceptable distances and/or spacing between balloons and/ormay have other station-keeping parameters that differ. By varying suchparameters from area to area, an exemplary network may provide anon-uniform topology, which may be desirable in a number of scenarios.

For example, FIG. 6A shows coverage of an exemplary balloon network thatspans a number of defined geographic areas, according to an exemplaryembodiment. In particular, FIG. 6A shows high-altitude balloons locatedover a region 600 that includes a city 602, suburbs 604, a rural area606, and an ocean 608. As such, station-keeping parameters forsuper-node balloons and/or sub-node balloons may vary between the city602, the suburbs 604, the rural area 606, and the ocean 608.

Note that in order to simplify the illustration, the super-node andsub-node balloons in FIG. 6A are shown in balloon clusters (BCs), whicheach include a super-node balloon and one or more sub-node balloons.FIG. 6B is a simplified illustration of a balloon cluster, according toan exemplary embodiment. In particular, FIG. 6B shows a balloon cluster601 that includes a super-node balloon 610 and sub-node balloons 620.The super-node balloon 610 is operable to communicate with each sub-node620 via an RF link. Further, while not shown, super-node balloon 610 isoperable to establish and communicate via one or more free-space opticallinks with one or more other super-node balloons.

The BCs shown in FIG. 6A may be arranged and operate in the same or asimilar manner to the balloon cluster 601 shown in FIG. 6B. Further,while FIG. 6A does not show free-space optical links between thesuper-nodes of the BCs, it should be understood that the super-nodeballoons in the BCs may function as part of a mesh network byestablishing free-space optical links with the super-node balloons inother BCs. For instance, in some implementations, the super-nodes withinthe BCs shown in FIG. 6A may serve as a backbone network, while thesub-nodes may provide access networks. More specifically, the sub-nodeballoons in a given BC may function as an access network, where eachsub-node provides a backhaul RF link to the super-node balloon in theBC.

In an exemplary implementation, station-keeping parameters for a givengeographic area may be used to form such BCs. For example,station-keeping parameters in city 602 may specify that each BC shouldinclude a super-node balloon and four sub-node balloons. Further, thestation-keeping parameters in city 602 may specify spacing for BCs. Notethat the formation of BCs may be accomplished via the station-keepingfunctionality for super-nodes and sub-nodes that effectively results inthe formation of BCs, rather than by defining station-keeping parametersspecifically for BCs.

For example, station-keeping parameters in city 602 may specify acertain distance range for adjacent sub-node balloons and/or a certaindensity of sub-node balloons, a certain distance range for adjacentsuper-node balloons and/or a certain density of super-node balloons. Thestation-keeping parameters in city 602 may also specify that eachsuper-node should move so as to be in RF communication range of acertain number of sub-node balloons (e.g., positioned so as to providean RF link with four sub-node balloons, or somewhere between three andfive sub-node balloons). Other examples of station-keeping parameters incity 602 are also possible.

By varying station-keeping functions in a given geographic area, thetopology of a balloon network may vary from area to area. For example,as shown in FIG. 6A, BCs in suburbs 604 are positioned such thatsuper-nodes and sub-nodes are less dense in suburbs 604, as compared toin the city 602.

To accomplish a less-dense topology in the suburbs 604, station-keepingparameters for the suburbs 604 may be set such that sub-nodes and/orsuper-nodes in the area are less dense in the suburbs. For instance, inthe suburbs 604, the upper and/or lower extent of the distance range foradjacent sub-node balloons may be greater, and/or the density ofsub-node balloons may be lower, as compared to the equivalentstation-keeping parameters in the city 602. Similarly, in the suburbs604, the upper and/or lower extent of the distance range for adjacentsuper-node balloons may be greater, and/or the density of super-nodeballoons may be lower, as compared to the equivalent station-keepingparameters in the city 602. Additionally or alternatively, the upperand/or lower extent of the acceptable distance range between asuper-node balloon and an adjacent sub-node balloon may be greater inthe suburbs 604 as compared to the equivalent station-keeping parametersin the city 602.

In a further aspect of the network topology of region 600, BCs in ruralarea 606 are positioned such that super-nodes and sub-nodes are evenless dense than in the suburbs 604. This may be accomplished by furthervarying station-keeping parameters in the manner described above.

Further, in the illustrated example, the station-keeping parameters forrural area 606 may be such that BCs over rural area 606 include moresub-nodes than the BCs over the city 602 and the suburbs 604. If thecapacity of a given free-space optical link is split among a greaternumber of backhaul links, then the capacity of each backhaul link may bereduced. For design and/or cost reasons, this may be acceptable invarious scenarios. For instance, if there is less bandwidth demand inrural 606, then decreasing the super-node to sub-node ratio may beacceptable. Other examples are possible. Further, in some scenarios, itis possible that the super-node to sub-node ratio may be reduced withoutaffecting the bandwidth of the backhaul links.

Further, note that in region 600, the only balloons illustrated as beingdeployed over the ocean 608 are super-node balloons. This topology mayalso be achieved via station-keeping functionality. For example,station-keeping parameters may specify that sub-nodes should attempt toremain positioned over land (e.g., over city 602, suburbs 604, and ruralarea 606). Further, station-keeping parameters may specify theacceptable distance range and/or the acceptable density range ofsuper-nodes over ocean 608.

Note that in practice, a network deployed over an ocean may very wellhave sub-node balloons as well as super-node balloons. More generally,while it is possible that a network may include only super-nodes over acertain region such as ocean 608, it is likely that most regions willalso include sub-node balloons.

In some implementations, the super-node balloons 609 over ocean 608 mayserve only to connect areas where sub-node balloons provide access tothe balloon network. In other implementations, the super-node balloons609 may be dually configured as super-nodes and sub-nodes. In such animplementation, the super-node balloons 609 may accordingly beconfigured for balloon-to-ground RF communications. Configured as such,the balloon may be accessed from ground-based stations in ocean 608(e.g., from an access point located on a boat). In otherimplementations, it is also possible that sub-node balloons may also bedeployed over an ocean (or another body of water), where demand fornetwork service is typically much lower.

It should be understood that because sub-node and super-node balloonsmay move throughout region 600 and relative to one another over time,the particular sub-nodes in the BC served by a given super-node balloonmay vary over time. As such, the sub-node balloons may function as anad-hoc network of access networks, where sub-nodes can move betweenaccess networks.

In a further aspect, while FIGS. 6A and 6B show each sub-node asbelonging to a single BC cluster, it is also possible that a givensub-node balloon could be part of access networks to multiplesuper-nodes (e.g., could be part of multiple BCs). In particular, asub-node could establish RF links with two or more super-nodes.

Furthermore, while all BCs in city 602 are shown as being identical, itshould be understood that the arrangement of BCs in city 602 may varywithin the station-keeping framework for city 602. For example, thedistance between a super-node and a sub-node may vary between thesub-nodes in a BC. As another example, the number of sub-nodes in a BCmay vary in city 602. Other examples of variations are possible.Further, similar variations may exist over the suburbs 604, the ruralarea 606, and/or the ocean 608.

In yet another aspect, station-keeping parameters in areas such as city602, suburbs 604, rural area 606, and/or ocean 608 may be updated inorder to dynamically change the topology of a balloon network. Forexample, FIG. 6C shows the same balloon network spanning the samegeographic areas as shown in FIG. 6A. However, in Figure C, the topologyof the balloon network has changed from that shown in FIG. 6B, accordingto updated station-keeping parameters in region 600.

In particular, FIG. 6C illustrates station-keeping functionality that isadapted to a weekend where a large music and art festival is occurringin rural area 606. Since it is the weekend and many individuals are notin city 602 for work, the service demands in city 602 may be reduced. Assuch, station-keeping parameters for city 602 may have been updated suchthat the density of super-node balloons and/or sub-node balloons isreduced in city 602. Further, station-keeping parameters may have beenupdated to define a new geographic area for the festival grounds 630.Thus, in an effort to increase the service capacity over the festivalgrounds 630, the station-keeping parameters for the festival grounds maybe defined so as to significantly increase the density of balloons overthe festival grounds 630.

Note that on the following Monday, when the festival has ended andpeople are returning to work in the city, station-keeping functionalitymay again be adjusted. For example, station-keeping parameters may beupdated such that the topology returns to a similar state as that shownin FIG. 6A. Other examples are also possible.

C. Mesh Network Functionality in a Hierarchical Balloon Network

Since balloons in an exemplary hierarchical balloon network maycollectively function as a mesh network, routing may involvedetermining: (a) a path between a ground-based station and a sourcesuper-node balloon data via one or more sub-node balloons, (b) a pathbetween the source super-node balloon and a target super-node balloon,which may be a single hop or may be a multi-hop path via one or moreother super-node balloons, and (c) a path between the target super-nodeballoon and a target ground-based station via one or more sub-nodeballoons.

Referring back to FIG. 4, to provide a specific example of routing in ahierarchical balloon network, consider an implementation whereground-based station 430E is an access point, and ground-based station430F is a gateway between hierarchical balloon network 400 and theInternet 460. As such, a first client device 440 may connect to theInternet 460 via ground-based station 430E and balloon network 400.Further, a second client device 450 may connect to the Internet 460, andthus may be connected to the balloon network 400 via ground-basedstation 430H.

In this scenario, the first client device 440 may send data to thesecond client device 450. When this occurs, data from client device 440may be routed from ground-based station 430E to super-node 410C viasub-nodes 420E and 420F.

Further, routing may involve path determination through the backbonenetwork of super-nodes to determine, e.g., a path from the sourcesuper-node to the target super-node. Thus, when data sent from the firstclient device 440 to the second client device 450 is received atsuper-node balloon 410C, a lightpath may be determined to the targetsuper-node balloon 410B. In the illustrated state of balloon network400, the determined lightpath may include optical links 402 and 404.

Various mesh routing techniques may be applied in order to route datathrough the super-nodes to a target super-node. (The target super-nodeis typically a super-node balloon with an RF link to a sub-node that isserving the target ground-based station.) For example, routing throughthe backbone network formed by the super-node balloons may beaccomplished in a similar manner as described in reference to theballoon networks illustrated in FIGS. 1 and 2. In other words, thesuper-nodes may be thought of as a distinct network for purposes ofrouting, such that paths between the super-node balloons andground-based stations via sub-node balloons may be determined separatelyfrom paths through the super-node balloons. Further, in someimplementations, a backup routing technique may be implemented such thatwhen a light path between two super-node balloons is down, full, orotherwise unavailable, a number of sub-node balloons can act as part ofthe mesh network and provide a lightpath or lightpaths between the twosuper-node balloons.

Further, as the super-nodes locations may change relative to the groundand relative to one another, the topology of the balloon network maychange over time. Accordingly, the routing technique may take intoaccount the current network topology.

In another aspect, note that in the above example, there is only onepath between ground-based station 430E and super-node 410C (i.e., themulti-hop path with RF links connecting ground-based station 430E,sub-node 420E, and sub-node 420F). As such, there is no pathdetermination needed as there is only one path between the ground-basedstation and the source super-node balloon. However, it is possible thatthere may be multiple paths between a ground-based station and a sourcesuper-node balloon. In this case, routing may involve path determinationbetween a ground-based station and a source super-node balloon.

For example, when the second client device 450 sends data to the firstclient device 440 via Internet 460, there are two paths betweenground-based station 430F and super-node 410B (e.g., via sub-node 420Hor sub-node 4200). As such, routing may involve path determination toselect between the available paths. Alternatively, a flooding techniquemay be used in which data is sent via all paths between a ground-basedstation and a source super-node.

In a further aspect, note that similar principals apply when routingdata between a target super-node balloon and a target ground basedstation, depending upon the topology of the one or more sub-nodeballoons connecting the target super-node balloon and a target groundbased station.

D. Multi-Layer Hierarchical Balloon Network

It should be understood that the description of a hierarchical balloonnetwork with super-node balloons and sub-node balloons is an example ofthe more general concept of a hierarchical balloon network with two ormore different types of balloons.

For example, an exemplary balloon network may be provided by a set ofballoons that include a number of first balloons and a number of secondballoons, which collectively operate as a hierarchical balloon network.In an exemplary embodiment, each of the first balloons includes afree-space optical communication system that is operable for datacommunications with one or more of the other first balloons. Thesuper-node balloons described herein are examples of such firstballoons. Further, each of the second balloons includes an RFcommunication system that is operable for data communications. Thesub-node balloons described herein are examples of such second balloons.

In an exemplary embodiment, at least one first balloon further includesan RF communication system that is operable to transmit data to at leastone second balloon. Further, the RF communication system of this secondballoon is operable to receive the data transmitted by the at least onefirst balloon and to transmit the received data to at least oneground-based station.

In a further aspect, an exemplary hierarchical balloon network mayfurther include additional types of balloons in addition to the firstand second balloons. The additional balloons may communicate with thefirst balloons via optical links and/or RF links. Additionally oralternatively, the additional balloons may communicate with the secondballoons via RF links.

IV. Conclusion

The particular arrangements shown in the Figures should not be viewed aslimiting. It should be understood that other embodiments may includemore or less of each element shown in a given Figure. Further, some ofthe illustrated elements may be combined or omitted. Yet further, anexemplary embodiment may include elements that are not illustrated inthe Figures.

Additionally, while various aspects and embodiments have been disclosedherein, other aspects and embodiments will be apparent to those skilledin the art. The various aspects and embodiments disclosed herein are forpurposes of illustration and are not intended to be limiting, with thetrue scope and spirit being indicated by the following claims. Otherembodiments may be utilized, and other changes may be made, withoutdeparting from the spirit or scope of the subject matter presentedherein. It will be readily understood that the aspects of the presentdisclosure, as generally described herein, and illustrated in thefigures, can be arranged, substituted, combined, separated, and designedin a wide variety of different configurations, all of which arecontemplated herein.

We claim:
 1. A system comprising: a plurality of first balloonsconfigured as nodes in a balloon network, wherein each of the firstballoons comprises a radio-frequency (RF) communication system that isoperable for communications with at least one ground-based station viaan RF link; and a plurality of second balloons configured as nodes in aballoon network, wherein each of the second balloons comprises afree-space optical communication system that is operable for datacommunications with one or more other second balloons via an opticallink, and wherein at least one of the second balloons further comprisesan RF communication system that is operable for data communications withat least one of the first balloons via an RF link.
 2. The system ofclaim 1, wherein both the second balloons and the first balloons arehigh-altitude balloons.
 3. The system of claim 1, wherein at least thesecond balloons are collectively operable as a mesh network.
 4. Thesystem of claim 3, wherein the mesh network comprises optical linksbetween second balloons.
 5. The system of claim 1, wherein the secondballoons and the first balloons are collectively operable as a meshnetwork, and wherein the mesh network comprises optical links betweensecond balloons and RF links between second balloons and first balloons.6. The system of claim 1, wherein the free-space optical communicationsystem of one or more of the second balloons comprises one or moreultra-bright light-emitting diodes that are operable to transmit afree-space optical signal.
 7. The system of claim 1, wherein thefree-space optical communication system of one or more of the secondballoons comprises a receiver that is operable to receive a free-spaceoptical signal.
 8. The system of claim 1, wherein the free-space opticalcommunication system of one or more of the second balloons comprises alaser system that is operable to transmit a free-space optical signal.9. The system of claim 1, further comprising at least one downlinkballoon, wherein the at least one downlink balloon comprises afree-space optical communication system that is operable to: (a)communicate with one or more of the second balloons and (b) communicatewith at least one ground-based station.
 10. The system of claim 1,wherein one or more of the second balloons and one or more of the firstballoons each comprise an altitude-control system that is operable toadjust altitude.
 11. The system of claim 10, wherein thealtitude-control system in each of the one or more second balloons andthe one or more of the first balloons is operable to change the altitudeof the respective balloon via adjustments to at least one of: (a) gasdensity of the respective balloon and (b) gas volume of the respectiveballoon.
 12. The system of claim 10, wherein each of the one or more ofthe second balloons and the one or more of the first balloons is furtheroperable to: use altitudinal wind data to determine a target altitudehaving wind that corresponds to a desired lateral movement of therespective balloon; and cause the altitude-control system to initiatealtitudinal movement of the respective balloon towards the targetaltitude in an effort to cause the desired horizontal movement of therespective balloon.
 13. The system of claim 1, wherein the secondballoons and the first balloons are collectively operable as a meshnetwork, and wherein each balloon is further operable to determine thedesired horizontal movement of the respective balloon based on a desiredtopology of the mesh network.
 14. The system of claim 1, wherein thesecond balloons and the first balloons are in substantially continuousmotion, and wherein the second balloons and the first balloons usealtitudinal adjustments to move so as to conform with station-keepingparameters.
 15. The system of claim 1, the second balloons and the firstballoons move based on one or more station-keeping parameters, whereinthe station-keeping parameters are based on a desired network topology.16. The system of claim 15, wherein the one or more station-keepingparameters comprise an acceptable distance range between any two of thesecond balloons and the first balloons.
 17. The system of claim 15,wherein the one or more station-keeping parameters comprise one or moreof: (a) an acceptable distance range between adjacent second balloons,(b) an acceptable distance range between adjacent first balloons, and(c) an acceptable distance range between a second balloon and anadjacent first balloon.
 18. The system of claim 15, wherein the one ormore station-keeping parameters comprise an acceptable amount ofdeviation from a desired density of the second balloons and the firstballoons.
 19. The system of claim 15, wherein the one or morestation-keeping parameters comprise one or more of: (a) an acceptableamount of deviation from a desired density of second balloons and (b) anacceptable amount of deviation from a desired density of first balloons,and (c) an acceptable distance range between a second balloon and anadjacent first balloon.
 20. The system of claim 15, wherein thestation-keeping parameters comprise a first set of station-keepingparameters for the second balloons and a second set of station-keepingparameters for the first balloons.
 21. The system of claim 15, whereinthe balloon network provides coverage in a plurality of definedgeographic areas, and wherein station-keeping parameters are separatelydetermined for each defined geographic area.
 22. The system of claim 1,wherein the second balloons collectively provide a backbone of theballoon network, and wherein the first balloons provide one or moreaccess networks for the balloon network.
 23. The system of claim 1,wherein station-keeping functionality of the second balloons and thefirst balloons is supported, at least in part, by a centralized controlsystem, wherein the centralized control system comprises one or moreground-based systems.
 24. The system of claim 23, wherein thecentralized control system comprises a central control system and one ormore regional control systems.
 25. The system of claim 1, whereinstation-keeping functionality of each of the second balloons and thefirst balloons is carried out, at least in part, by the respectiveballoon.
 26. A system comprising: a plurality of balloons thatcollectively operate as a hierarchical balloon network, wherein theplurality of balloons comprise at least a plurality of first balloonsand a plurality of second balloons; wherein each of the first balloonscomprises a radio-frequency (RF) communication system that is operablefor communications with at least one ground-based station; and whereineach of the second balloons comprises a free-space optical communicationsystem that is operable for packet-data communication with one or moreother second balloons, and wherein at least one of the second balloonsfurther comprises an RF communication system that is operable totransmit data to at least one of the first balloon.
 27. The system ofclaim 26, wherein the plurality of balloons that collectively operate asthe hierarchical balloon network further comprise one or more othertypes of balloons, in addition to the first and second balloons.
 28. Thesystem of claim 26, wherein the plurality of balloons that collectivelyoperate as the hierarchical balloon network are high-altitude balloons.29. The system of claim 26, wherein at least the second balloons arecollectively operable as a mesh network.
 30. The system of claim 29,wherein the mesh network comprises optical links between secondballoons.
 31. The system of claim 26, wherein the hierarchical balloonnetwork is a hierarchical mesh network, and wherein the hierarchicalmesh network comprises optical links between the second balloons and RFlinks between the second balloons and the first balloons.
 32. The systemof claim 26, wherein one or more of the first balloons and one or moreof the second balloons each comprise an altitude-control system that isoperable to adjust altitude.
 33. The system of claim 32, wherein each ofthe one or more first balloons and the one or more second balloons thatcomprises an altitude-control system is further operable to: usealtitudinal wind data to determine a target altitude having wind thatcorresponds to a desired lateral movement of the respective balloon; andcause the altitude-control system to initiate altitudinal movement ofthe respective balloon towards the target altitude in an effort to causethe desired horizontal movement of the respective balloon.